Conventionally, for an exhaust system for an internal combustion engine, for example, there is known an exhaust gas recirculation system (EGR system) that recirculates (flows back) exhaust gas (hereinafter referred to as EGR gas) from an exhaust pipe through an exhaust gas recirculation pipe into an intake pipe of an internal combustion engine (engine) for the purpose of reducing harmful substances (e.g., nitrogen oxide: NOx) contained in exhaust gas discharged from a cylinder of the engine for traveling of a vehicle such as an automobile.
In the EGR system, there is disposed an EGR gas flow rate control valve (hereinafter referred to as an EGR control valve) for variably controlling a flow rate of EGR gas flowing through a EGR flow passage in the exhaust gas recirculation pipe is disposed (see, e.g., WO/2012/126876). This EGR control valve includes an electric motor having a motor shaft and a pinion gear, an intermediate shaft having an intermediate gear which rotates in engagement with the pinion gear, an eccentric shaft having an output gear which rotates in engagement with the intermediate gear, and an eccentric, and a connecting link with a poppet valve, a valve stem, and the eccentric in engagement with each other. The intermediate shaft is disposed laterally as well as near the eccentric shaft such that the eccentric and the connecting link are arranged near the electric motor.
In the conventional EGR control valve, a housing wall does not exist between the output gear and the eccentric, and it is difficult to arrange bearings for slidably supporting the eccentric shaft in its rotation direction. Accordingly, there is caused an insufficient engagement between the intermediate gear and the output gear due to axial deflection of the eccentric shaft. As a result, there is an issue that power of the electric motor is not transmitted effectively to the eccentric and the poppet valve.